Plasma processing is a technique that is necessary to manufacture semiconductor devices. Recently, due to demands for high-integration and high-speed of LSI (Large Scale Integrated circuit), a design rule of the semiconductor devices constituting the LSI is further miniaturized, and a semiconductor wafer is scaled up. Accordingly, a plasma processing apparatus needs to cope with such miniaturization and scaling up.
As for the plasma processing apparatus, a parallel plate type plasma processing apparatus or an inductively coupled plasma processing apparatus has been conventionally used. In that case, however, a generated plasma has a high electron temperature and, thus, fine devices are damaged.
Further, since a region having a high plasma density is limited, it is difficult for the parallel plate type plasma processing apparatus or the inductively coupled plasma processing apparatus to uniformly and quickly perform plasma processing on a scaled-up semiconductor wafer.
Accordingly, an RLSA (registered trademark) microwave plasma processing apparatus capable of uniformly generating a surface wave plasma having a high density and a low electron temperature attracts attention (see, e.g., Japanese Patent Application Publication No. 2000-294550).
In the RLSA microwave plasma processing apparatus, a planar slot antenna having a plurality of slots formed in a predetermined pattern is provided, as a microwave radiating antenna for radiating a microwave for generating a surface wave plasma, at an upper portion of a chamber. A microwave generated from a microwave generation source is radiated from the slots of the antenna into the chamber maintained in a vacuum state through a microwave transmission plate that is made of a dielectric material and forms a ceiling wall of the chamber. A surface wave plasma is generated in the chamber by a microwave magnetic field. Accordingly, a target object such as a semiconductor wafer or the like is processed.
Meanwhile, PCT Publication No. 2008/013112 discloses a plasma source for dividing a microwave into a plurality of microwaves, guiding microwaves radiated from a plurality of microwave radiation mechanisms provided at a top surface of the chamber into a chamber and spatially combining a plasma in the chamber, each of the microwave radiation mechanisms having the above-described planar antenna and a tuner for matching an impedance. By spatially combining the plasma by using the plurality of microwave radiation mechanisms, it is possible to individually control phases and intensities of the microwaves introduced from the microwave radiation mechanism and also possible to relatively easily control plasma distribution.
In the apparatuses disclosed in Japanese Patent Application Publication No. 2000-294550 and PCT Publication No. 2008/013112, a processing gas and an excitation gas such as Ar gas are supplied from a sidewall of the chamber into the chamber during plasma processing. Therefore, the controllability of flow of the processing gas or the excitation gas in the chamber is poor and it is difficult to uniformly introduce the processing gas or the excitation gas. As a solution to such problems, Japanese Patent Application Publication No. 2012-216525 discloses a technique for introducing a gas from a ceiling wall of the chamber.
When the excitation gas and the processing gas are introduced into the chamber, an appropriate dissociation state suitable for properties of gases is required. For example, in the case of forming a SiN film by plasma CVD using SiH4 gas as a processing gas and a nitriding gas such as N2 gas, NH3 gas or the like, Ar gas or the nitriding gas such as N2 gas, NH3 gas or the like requires energy that is enough for excitation and dissociation, whereas excessive dissociation of the SiH4 gas needs to be prevented. However, in the case of introducing gas from the ceiling wall of the chamber as disclosed in Japanese Patent Application Publication No. 2012-216525, it is not possible to prevent introduction of gas into a high electron temperature region. Thus, the gas such as SiH4 gas or the like, which is not intended to be excessively dissociated, is also excessively dissociated. Accordingly, gaseous particles are generated or a nozzle is clogged.
On the other hand, Japanese Patent Application Publication No. 2008-47883 discloses a microwave plasma processing apparatus including an upper shower plate provided at a ceiling wall for introducing a microwave and a lower shower plate provided between the upper shower plate and a target substrate. An excitation gas such as Ar gas or the like or a gas to be actively dissociated is introduced from the upper shower plate. A gas which is not intended to be excessively dissociated, such as SiH4 gas or the like, is introduced from the lower shower plate. In other words, the microwave plasma processing apparatus generates a surface wave plasma by introducing a microwave into a chamber from a ceiling wall. Since, however, an electron temperature of a plasma is highest at a portion directly below the ceiling wall and abruptly decreased at a plasma diffusion region spaced from the ceiling wall, a dissociation state suitable for properties of gases can be realized by utilizing a difference in the electron temperature depending on positions in the chamber.
However, in the microwave plasma processing apparatus disclosed in Japanese Patent Application Publication No. 2008-47883, the lower shower plate has a gas channel and a plurality of openings through which a plasma passes, and the processing gas is introduced from a gas supply port formed at a sidewall of the chamber. Therefore, diffusion of the plasma is disturbed by the gas supply port and the gas channel. Accordingly, in the microwave plasma processing apparatus disclosed in Japanese Patent Application Publication No. 2008-47883, a plasma density becomes insufficient, which makes it difficult to obtain a desired film forming rate or film quality controllability. In addition, the uniformity of the plasma becomes insufficient, so that desired in-plane uniformity of the plasma processing may not be obtained.